T-ALL characteristics are under BM niches influence. (A) Leukemic cell production starting from freshly purified hT-ALL cells derived from thoracic or tail vertebrae BM after short-term (left; day 7) or (B) long-term (right; day 28) coculture with MS5-DL1 stromal cells. Shown are means ± SEM of triplicate cultures. (C) Kinetic of leukemia development in secondary mice after transplantation of 500 hT-ALL#1 cells recovered from thorax (red) and tail (blue) vertebrae. Secondary transplantations of hT-ALL#2 and hT-ALL#3 are provided in supplemental Figure 3. (D) Limiting dilution transplantation of 3 hT-ALL (#1-#3) isolated from thoracic or tail BM into secondary mice (from 5 × 10⁴ cells to 50 cells per mouse). T-ALL development was monitored using iterative femur samplings. Positive mice contain more than 90% hCD45⁺/hCD7⁺ T-ALL cells. (E) Human hCD7 cell-surface expression of hT-ALL recovered in tail and thorax vertebrae from secondary mice (IIr, 19 mice) transplanted with hT-ALL isolated from primary (Ir) mouse tail and thorax. (F) Thorax- and tail-derived hT-ALL#1 cells were grown in coculture with MS5-DL1 cells for 12 days before transplantation into secondary mice (500 cells/mouse, 4 mice/niche). Kinetic of hT-ALL engraftment in the femurs of mice is shown. Representative of 2 experiments. Mean data (± SEM) are indicated. Statistics are calculated according to nonparametric Mann-Whitney U test (*P < .05; ***P < .001).